Magnetic field sensor

ABSTRACT

A magnetic field sensor including an amplifier and a magnetic field element for outputting a signal to a switch circuit according to the strength of an applied magnetic field. The switch circuit outputs a signal selected by an external two-phase signal to an amplifier that amplifies the signal and outputs a resulting voltage to a first end of a memory element. A switch, having one end connected to a second end of the memory element, is controlled by the two-phase signal. The switch closes in a first phase of the two-phase signal causing the memory element to store the output voltage of the amplifier, and opens in a second phase causing a vector sum of the output voltage the amplifier to be stored in the memory element and providing the output voltage to a signal output terminal connected to the second end of the memory element.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetic field sensor which comprisesa Hall element and an amplifier for amplifying the output voltage of theHall element and which detects the magnetic field strength in theinstalled location so as to output a signal in accordance with thedetected magnetic field strength.

A typical magnetic field sensor is a bipolar IC or a CMOS IC whichinclude a Hall element for outputting an output voltage proportional tothe magnetic field strength and an amplifier for amplifying an outputvoltage of the Hall element as well as a comparator for inputting theoutput voltage of the amplifier to be compared with a referencepotential and for outputting the comparison result. Such a magneticfield sensor outputs an output signal of two values (0 or 1) showingwhether the magnetic field strength of the location where the magneticfield sensor is installed is larger or smaller than a constantreference.

Another magnetic field sensor comprises a Hall element for outputtingthe output voltage proportional to the magnetic field strength and anamplifier for amplifying the output voltage of the Hall element andoutputs the output signal of that amplifier as an analog signal, withoutchange.

One of the major factors of dispersion in characteristics among theproducts of the magnetic field sensor is the dispersion of the offsetsignal component included in the output voltage of the Hall element.This occurs due to the stress, or the like, which is received by theHall element body from the package. Another one is an offset signalcomponent which exists at the input terminal of the amplifier (ingeneral, a differential amplifier).

U.S. Pat. No. 4,037,150 discloses a technology which makes the influenceof the offset signal component of the Hall element be small. A magneticfield sensor according to the invention described in U.S. Pat. No.4,037,150 has a Hall element in a plate form with four terminals and theform of a Hall element is geometrically equal, as is that of the Hallelement 1 described in FIGS. 5 and 6.

“Geometrically equal forms” means that the form under the condition ofFIG. 5 and the form under the condition where the Hall element of FIG. 5is rotated by 90 degrees (it is rotated so that A-A′ agrees with B-B′ inFIG. 5) are the same, as is the Hall element 1 described in FIG. 5.

A description is made in reference to FIG. 5. The Hall element has twopairs of terminals A-A′ and B-B′ in the diagonal direction. In the firstphase (first timing) a power source voltage is applied across theterminals A-A′ and the output voltage across the terminals B-B′ isdetected so as to be stored in memory. Next, a power source voltage isapplied across the terminals B-B′ at the second phase (second timing)and the output voltage across the terminals A-A′ is detected so as to bestored in memory. The switching of these actions is implemented by theswitch circuit 24.

Here, a circuit for applying a power source voltage to the Hall elementis not shown in every figure.

The timing chart for the first and the second phases is described inFIG. 7. A sum is gained between an output signal of the first phase andan output signal of the second phase and, then, an effective signalcomponent of an output signal of the Hall element is added in the samephase so as to be doubled while an offset signal component of an outputsignal of the Hall element is added in the negative phase so as to bemutually canceled. In this manner, the influence given to the outputsignal by the offset signal component of the Hall element is suppressed.

Next, the configuration of a conventional magnetic field sensor whichcompensates the offset signal component due to the input offset of theamplifier is described in reference to FIGS. 5 and 6.

FIG. 5 shows a configuration of a magnetic field sensor according to thefirst prior art as disclosed in the Japanese unexamined patentpublication H8(1996)-201491. In FIG. 5, a Hall element is denoted as 1,a switch circuit is denoted as 24, capacitors which are memory elementsare denoted as 4 and 6, switches are denoted as 5 and 8, voltage-currentconversion amplifiers, each of which has high input and output impedanceand converts a input voltage into a current so as to be outputted, aredenoted as 10 and 11, and a resistance is denoted as 12.

In the first phase, the first phase signal (a) which has a pulse isgiven to the switch 5 while in the second phase, the second phase signal(b) which has a pulse is given to the switch 8. In addition, the firstand the second phase signals are given to the switch circuit 24.

The relationship between the first phase and the second phase in thefirst prior art is shown in FIG. 7.

The operation in the first phase is described.

In the first phase the switch 5 is closed while the switch 8 is open. Atthis time, a power source voltage is applied across the terminals A-A′of the Hall element 1 so that the output voltage across the terminalsB-B′ is outputted through the switch circuit 24. The output voltage ofthat Hall element 1 is inputted to the voltage-current conversionamplifier 10.

The voltage-current conversion amplifier 10 outputs a current which isproportional to the output voltage of the Hall element 1. The outputcurrent IOUT of the voltage-current conversion amplifier 10 isrepresented as in the following equation.

IOUT=α(Vh+Voff 10)  (1)

Voff10 is an input offset voltage of the voltage-current conversionamplifier 10 and Vh is an output voltage of the Hall element (inputvoltage of the voltage-current conversion amplifier 10). α is aconversion coefficient (proportional constant) from voltage to current.

The resistance value of a Hall element has a great dispersion amongproducts. In general, when the resistance value of a Hall element issmall, the output voltage of the Hall element becomes large and when theresistance value of the Hall element is large, the output voltage of theHall element becomes small.

This current flows into the capacitors 4 and 6 via the switch 5. Avoltage-current conversion amplifier 11 which has the same functions asthe amplifier 10 generates a current which is proportional to adifferential voltage between the charging voltage of the capacitor 4 andthe charging voltage of the capacitor 6 and which is in the oppositedirection to the direction of a current of the voltage-currentconversion amplifier 10. Charging current to the capacitors 4 and 6stops when the sum of the respective output currents of thevoltage-current conversion amplifiers 10 and 11 becomes zero. At thistime, since the directions of the output currents of the respectivevoltage-current conversion amplifiers 10 and 11 are opposite to eachother, the absolute values of the respective output currents of thevoltage-current conversion amplifiers 10 and 11 agree. Accordingly, theoutput current IOUT2 of the voltage-current conversion amplifier 11 canbe represented in the following equation.

IOUT 2=−α(Vh+Voff 10)  (2)

Next, the operation in the second phase is described.

In the second phase, the switch 5 is open and the switch 8 is closed. Atthis time, since the charging and discharging currents for thecapacitors 4 and 6 do not flow, the capacitors 4 and 6 maintain thecharges (accordingly, voltage) stored in the first phase. Accordingly,the voltage-current conversion amplifier 11 makes the current of thesame value as of the current in the first phase keep flowing. The outputcurrent IOUT2 of the voltage-current conversion amplifier 11 isrepresented in the equation (2).

At this time, a power source voltage is applied across the terminalsB-B′ of the Hall element 1 so that the output voltage across theterminals A-A′ is outputted through the switch circuit 24. The outputvoltage of that Hall element 1 is inputted into the voltage-currentconversion amplifier 10. The output signal of that Hall element whichhas been inputted into the voltage-current conversion amplifier 10 issubstantially in the opposite direction to that at the time of the firstphase. Accordingly, at this time, the output current of thevoltage-current conversion amplifier 10 becomes of the same amount andof the same polarity as of the output current of the voltage-currentconversion amplifier 11.

The output current IOUT1 of the voltage-current conversion amplifier 10in the second phase can be represented in the following equation.

IOUT 1=α(−Vh+Voff 10)  (3)

The sum current of the output currents of the voltage-current conversionamplifiers 10 and 11 flows into the resistance 12 via the switch 8.

Therefore, the current I which flows into the resistance 12 is gained byadding the equation (2) and the equation (3) as:

I=IOUT 1+IOUT 2=−2αVh  (4)

which shows that the input offset voltage Voff10 is canceled.

FIG. 6 shows the second configuration example of a conventional magneticfield sensor. In FIG. 6, a Hall element is denoted as 1, a switchcircuit is denoted as 24, a voltage amplifier is denoted as 25,capacitors which are memory elements are denoted as 4 and 6, andswitches are denoted as 5, 8 and 9. The capacitance values of thecapacitors 4 and 6 are equal.

The relationship among the first phase, the second phase and the thirdphase according to the second prior art is shown in FIG. 8.

The operation in the first phase is described.

In the first phase, the switch 5 is closed while the switches 8 and 9are open.

At this time, power source voltage is applied across the terminals A-A′of the Hall element 1 so that the output voltage across the terminalsB-B′ is outputted through the switch circuit 24. The output voltage ofthat Hall element 1 is inputted into the voltage amplifier 25.

The voltage amplifier 25 outputs the voltage proportional to the outputvoltage of the Hall element 1. The output voltage V1 of the voltageamplifier 25 in the first phase can be represented in the followingequation.

V 1=β(Vh+Voff 25)  (5)

Voff25 is an input offset voltage of the voltage amplifier 25 and Vh isan output voltage of the Hall element (input voltage of the voltageamplifier 25). β is a voltage amplification factor of the voltageamplifier 25.

The capacitor 4 is charged to the output voltage V1 of the voltageamplifier 25 via the switch 5.

Next, the operation in the second phase is described.

In the second phase, the switch 8 is closed while the switches 5 and 9are open.

A power source voltage is applied across the terminals B-B′ of the Hallelement 1 so that the output voltage across the terminals A-A′ isoutputted through the switch circuit 24. The output voltage of that Hallelement 1 is inputted into the voltage amplifier 25. An output signal ofthat Hall element which is inputted into the input terminal of thevoltage amplifier 25 becomes substantially of the opposite direction tothat at the time of the first phase. Accordingly, at this time, theoutput voltage V2 of the voltage amplifier 25 can be represented in thefollowing equation.

V 2=β(−Vh+Voff 25)  (7)

The capacitor 6 is charged to the output voltage V2 of the voltageamplifier 25 via the switch 8.

Finally, the operation in the third phase is described.

In the third phase, the switch 9 is closed while switches 5 and 8 areopen.

Both terminals of the capacitor 4 are made to cross each other via theswitch 9 and are connected in parallel with both terminals of thecapacitor 6. As a result, the average value of the voltage −V1, acrossthe terminals of the capacitor 4, and the voltage V2, across theterminals of the capacitor 6, is outputted to the output terminal. Sincethe capacitance values of the capacitors 4 and 6 are the same, thatoutput voltage V is represented in the following equation.

V=(−V 1+V 2)/2=−βVh  (8)

Here, it is seen that the input offset voltage Voff25 of the voltageamplifier 25 is canceled.

The voltage amplifier 25 of the magnetic field sensor, which utilizes aHall element, outputs the first output signal which is a signal gainedby amplifying the output signal across the two mutually facing terminalsof the Hall element with four terminals in the first phase. The voltageamplifier 25 outputs the second output signal which is a signal gainedby amplifying the output signal across the other two mutually facingterminals of the Hall element with four terminals in the second phase.This second output signal is substantially a signal gained by invertingthe first output signal. In this manner, the voltage amplifier of amagnetic field sensor which utilizes a Hall element cancels the inputoffset voltage Voff25 of the voltage amplifier 25 by outputting signalsin the first phase and in the second phase which are in a substantiallyinverted relationship.

Since the output voltage of the Hall element is outputted as adifferential voltage between the two terminals of the Hall element,conventionally the differential voltage of the Hall element is inputtedinto a differential amplifier so that the differential amplifier outputsa non-inverted (plus) output signal and an inverted (minus) outputsignal.

Therefore, an amplifier of a conventional magnetic field sensor is adouble output-type amplifier which has a non-inverted output terminaland an inverted output terminal as shown in FIG. 5 or 6.

When the double output-type amplifier is used, however, the output parthas a large number of component elements and a large chip area isoccupied.

In a conventional configuration, there is the defect that the circuitscale for canceling the input offset voltage is large.

In addition, a magnetic field sensor has been used in products which arebattery operated, such as cellular phones, in recent years and,therefore, the reduction of the consumption current of the magneticfield sensor is becoming an important technical problem. As for themeans used for the reduction of the consumption current, it is generalto adopt an intermittent operation which makes the consumption currentbe zero during a constant time by using a counter, or the like.

However, there is a constraint in the time wherein the sensor operationcan be stopped depending on the sets using the magnetic field sensorand, therefore, it becomes a problem of in how many steps one sensingoperation can be implemented. More concretely, in the first prior art,the magnetic field strength can be measured in the two steps of thefirst and the second phases. In the second prior art the magnetic fieldstrength can be measured in the three steps of the first to the thirdphases.

The present invention is intended to solve the above describedconventional problem and has the purpose of providing a magnetic fieldsensor which reduces the dispersion of the output voltage for detectingthe magnetic field strength and which consumes a small amount of powerand is inexpensive.

SUMMARY OF THE INVENTION

The invention according to claim 1 of the present invention is amagnetic field sensor comprising:

a Hall element for outputting a signal in accordance with an appliedmagnetic field strength to an output terminal;

a switch circuit for inputting the signal of said output terminal ofsaid Hall element and for outputting a signal selected by a signalcomprising first and second phases given from the outside of said switchcircuit;

an amplifier wherein at least one input terminal is connected to theoutput terminal of said switch circuit and a voltage gained amplifyingthe signal of this input terminal is outputted to an output terminal;

a first memory element of which one end is connected to said outputterminal of said amplifier;

a switch of which one end is connected to the other end of said firstmemory element and which carries out opening and closing operations bymeans of said signal which comprises the first and the second phasesgiven from the outside of said switch; and

a signal output terminal connected to said other terminal of said firstmemory element,

wherein said switch closes in said first phase so that said first memoryelement stores an output voltage of said amplifier and said switch opensin said second phase so that a vector sum of said voltage stored in saidfirst memory element then an output voltage of said amplifier isoutputted to said output terminal.

The present invention cancels the input offset voltage of the amplifierin a simple circuit. Thereby, a compact and inexpensive magnetic fieldsensor which receives no influence from that input offset voltage andwhich has little dispersion among products is attained.

In addition, the present invention attains a magnetic field sensor whichconsumes a small amount of power.

In the present specification and in the scope of the claims, the word“phase” means a timing along the time axis. The words “first phase” and“second phase” mean no more than being of mutually different timingalong the time axis.

For example, in addition to the case where the “first phase” and the“second phase” occur repeatedly as in FIG. 7, or the like, the casewhere they occur only once when there is a request from the outside isincluded in the technical scope of the present invention.

Furthermore, in the present invention, the period of the repetition inthe case that the “first phase” and the “second phase” occur repeatedlyas in FIG. 7 or the like, the ratio of the length of the period of thefirst phase to that of the second phase, the length of the period whichbelongs to neither the first phase nor the second phase, or the like, donot matter. For example, a case where a magnetic field sensor isintermittently operated at long constant intervals is also included.

The invention according to claim 2 of the present invention is amagnetic field sensor according to claim 1, characterized in that:

said switch circuit comprises second and third memory elements; and

in said first phase of said signal given from the outside of said switchcircuit, the output voltage of the output terminal of said Hall elementis stored in said second memory element and the voltage stored in saidthird memory element is given to said amplifier and, in said secondphase, the voltage stored in said second memory element is given to saidamplifier and the voltage of the output terminal of said Hall element isstored in said third memory element.

According to the present invention, in a simple circuit configuration,the differential voltage between the two terminals of the Hall elementis, for example, converted into a voltage relative to the potential ofone output terminal of the magnetic sensor so that the voltage relativeto the potential of this one output terminal is inputted into a singleoutput-type amplifier. The potential of this one output terminal may bea constant reference potential (including the ground) or may not be areference potential.

In the present invention, a single output-type amplifier can be utilizedin place of a conventional double output-type amplifier. The presentinvention wherein a single output-type amplifier is used has a smallernumber of component elements of the output part than that of a doubleoutput-type amplifier and, therefore, occupies only a small chip area.

The present invention can attain a compact and inexpensive magneticfield sensor with a low power consumption.

The single output-type amplifier amplifies the inputted signal andoutputs either one of the non-inverted output signal or the invertedoutput signal.

The invention according to claim 3 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in thatat least one memory element among said memory elements is a capacitor.

According to the present invention, a magnetic field sensor uses amemory element, which is compact so as to be suitable for an IC.Thereby, a compact and inexpensive magnetic field sensor can beattained.

The invention according to claim 4 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in that:

said switch comprises first, second and third parallel connectionswherein first and second conductive characteristics transistors areconnected in parallel, and the connection between two terminals of saidfirst and second conductive characteristics transistors are conducted orcut off by a binary signal given from the outside of said switch,

wherein both ends of the second parallel connection are connected to oneend of the first parallel connection; and both ends of the thirdparallel connection are connected to the other end of the first parallelconnection; and the first conductive characteristics transistor in thefirst parallel connection is driven by a different value of the binarysignal from a value of the binary signal for driving the firstconductive transistors in the second and third parallel connections; andthe second conductive characteristics transistor in the first parallelconnection is driven by a different value of the binary signal from avalue of the binary signal for driving the second conductive transistorsin the second and third parallel connections.

According to the present invention, for example, at the time when aswitch of MOS structure opens or closes in accordance with the change ofthe gate terminal of the switch, the charge stored in the parasiticcapacitor across the gate and the source or across the gate and thedrain of the switch can be prevented from flowing out into or flowing infrom the memory element.

Thereby, a magnetic field sensor with little dispersion can be attained.

The invention according to claim 5 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in thatat least one of the resistances for defining the gain of the amplifieris an element of which the manufacturing process is identical to that ofthe Hall element.

In a magnetic field sensor according to the present invention, at leastone resistance among the resistances for defining the gain of thevoltage amplifier is formed of an element of which the manufacturingprocess is identical to that of the Hall element, and the Hall elementand the voltage amplifier are included in the same semiconductor chip.

When the resistance value of a Hall element is small, the resistancevalue of the resistance made of this identical element becomes small andthe magnetic field sensor is configured so that the gain of the voltageamplifier becomes small as a result. On the contrary, when theresistance value of the Hall element is large, the resistance value ofthe resistance made of this identical element becomes large and the gainof the voltage amplifier becomes large as a result.

Thereby, the effect is obtained that a magnetic field sensor can beattained wherein the dispersion of the output voltage is smaller thanthe dispersion of the resistance value of the Hall element.

In the description of the present specification and the scope of theclaims, “element of which the manufacturing process is identical” meansan element produced through the same manufacturing process. For example,it means to go through the diffusion step of the identical impurities orto produce the identical N well. The differences in physical dimensionsor forms of the elements do not matter. Accordingly, in the case that aHall element and a resistance are the elements manufactured through theidentical manufacturing process, they are the elements of which themanufacturing processes are identical even if the dimensions or theforms of the Hall element and the resistance are different.

The invention according to claim 6 of the present invention is amagnetic field sensor characterized by comprising:

a Hall element which outputs a signal in accordance with an appliedmagnetic field strength;

an amplifier which amplifies the output signal of this Hall element andoutputs a voltage signal across a pair of output terminals;

a condenser of which both ends are connected to the pair of the outputterminals of said amplifier;

a switch part which is inserted and makes a connection between one ofsaid output terminals in the pair and one terminal of said condenser andwhich is closed by a first signal given from the outside of said switchpart and is opened by a second signal given from the outside of saidswitch part; and

an output terminal which outputs the voltages of both ends of saidswitch, respectively,

wherein the polarities of the voltage signals for the pair of the outputterminals of said amplifier during the period of said first signal andduring the period of said second signal are mutually oppositepolarities.

The present invention cancels the input offset voltage of the amplifierwith a simple circuit. Thereby, a compact and inexpensive magnetic fieldsensor is attained which receives no influence of this input offsetvoltage and which has little dispersion among products.

The invention according to claim 7 of the present invention is amagnetic field sensor characterized by comprising:

a Hall element which outputs signals to first and second terminal pairsin accordance with an applied magnetic field strength;

first and second condensers;

a first connection part which connects terminals of said first terminalpair and both ends of said first condenser, respectively;

a second connection part which connects terminals of said secondterminal pair and both ends of said second condenser, respectively;

a first switch part which is inserted and makes a connection in saidfirst connection part and which closes this first connection part bymeans of a first signal given from the outside of said first switch partand opens this first connection part by means of a second signal givenfrom the outside of said first switch part;

a second switch part which is inserted and makes a connection in saidsecond connection part and which opens this second connection part bymeans of said first signal given from the outside of said second switchpart and closes this second connection part by means of said secondsignal given from the outside of said second switch part;

an amplifier which amplifies a signal given to an input terminal so asto output to an output terminal;

a first output terminal;

a third connection part which connects both ends of said first condenserto the input terminal of said amplifier as well as to said first outputterminal, respectively;

a fourth connection part which connects both ends of said secondcondenser to the input terminal of said amplifier as well as to saidfirst output terminal, respectively;

a third switch part which is inserted and makes a connection in saidthird connection part and which opens this third connection part bymeans of said first signal given from the outside of said third switchpart and closes this third connection part by means of said secondsignal given from the outside of said third switch part:

a fourth switch part which is inserted and makes a connection in saidfourth connection part and which closes this fourth connection part bymeans of said first signal given from the outside of said fourth switchpart and opens this fourth connection part by means of said secondsignal given from the outside of said fourth switch part;

a second output terminal;

a third condenser of which one end is connected to the output terminalof said amplifier and of which the other end is connected to said secondoutput terminal; and

a fifth switch part of which both ends are connected respectively tosaid first and second output terminals and which is closed by said firstsignal given from the outside of said fifth switch part and is opened bysaid second signal given from the outside of said fifth switch part;

wherein a signal is extracted across said first and second outputterminals.

The present invention converts a differential voltage between twoterminals of the Hall element into a voltage from the potential of oneoutput terminal of the magnetic field sensor with a simple circuitconfiguration, and inputs this voltage from the potential of one outputterminal of the magnetic field sensor into a single output-typeamplifier. As for the amplifier which amplifies the voltage from thepotential of one output terminal of the magnetic field sensor, a singleoutput-type amplifier can be utilized.

The potential of one output terminal of the magnetic field sensor may bea constant reference potential or may not be a constant referencepotential.

The present invention cancels the input offset voltage of the amplifierwith a simple circuit. Thereby, a compact and inexpensive magnetic fieldsensor is attained which receives no influence of this input offsetvoltage and which has little dispersion among products.

The invention according to claim 8 of the present invention is amagnetic field sensor according to claim 7, characterized by comprising:

a comparator that converts the results of the comparison of thedifferential signal of said input signals which enter from said firstoutput terminal and said second output terminal respectively with apredetermined voltage into binary signals so as to output; and

a latch circuit which inputs the output signal of said comparator andsaid second signal, and outputs either value of said binary signal,synchronized with one phase of said second signal.

The invention according to claim 8 can, additionally, latch the inputvoltage at the timing when the second phase ends and can output aconstant digital value of 0 or 1.

The invention according to the present invention is a magnetic fieldsensor characterized by comprising:

a Hall element which outputs a signal in accordance with an appliedmagnetic field strength;

an amplifier which amplifies the output signal of this Hall element andoutputs a voltage signal to an output terminal pair;

a condenser of which respective terminals are connected to the terminalsof the output terminal pair of said amplifier;

a switch which is inserted to make a connection with one terminal ofsaid output terminal pair and one terminal of said condenser and whichis closed by a first signal given from the outside of said switch and isopened by a second signal given from the outside of said switch;

output terminals which output voltages of both ends of said switchrespectively;

a comparator which inputs signals of these output terminals respectivelyand converts the results of the comparison of the differential signal ofsaid input signals with a predetermined voltage into a binary signal soas to output; and

a latch circuit which inputs said binary signal and said second signal,and outputs either value of said binary signal, synchronized with onephase of said second signal,

wherein the polarities of the voltage signals of the output terminalpair of said amplifier between the period of said first signal and theperiod of said second signal are of mutually opposite polarities.

The invention can cancel the input offset voltage of the amplifier witha simple circuit and can latch the input voltage at the timing when thesecond phase ends so as to output a constant digital value of 0 or 1.

The invention according to the present invention is a magnetic fieldsensor, characterized in that predetermined voltage of said comparatorvaries depending on the output signal of said latch circuit.

The invention can extract from a comparator, a signal which is stableagainst noise signals and of which the chattering is suppressed byproviding the reference value set for the judgment by the comparatorwith a hysteresis. By giving this signal to a latch circuit, a stablesignal which has a high judgment precision can be extracted from thelatch circuit.

Though the novel characteristics of the invention are nothing more thanthe particular description in the attached claims, the present inventionwith respect to both the configuration and the contents, together withother purposes or characteristics, will be better understood andevaluated by means of the following detailed description which is to beunderstood in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of a magnetic field sensor accordingto the first embodiment of the present invention;

FIG. 2 is a configuration diagram of a magnetic field sensor accordingto the second embodiment of the present invention;

FIG. 3 is a configuration diagram of a magnetic field sensor accordingto the third embodiment of the present invention;

FIG. 4 is a configuration diagram of a switch according to the presentinvention;

FIG. 5 is a configuration diagram of a magnetic field sensor accordingto the first prior art;

FIG. 6 is a configuration diagram of a magnetic field sensor accordingto the second prior art;

FIG. 7 is a timing chart according to the first prior art as well as thefirst, the second and the third embodiments; and

FIG. 8 is a timing chart according to the second prior art.

It must be taken into account that part of, or the entirety of, thedrawings are depicted in schematic representation for the purpose ofillustration and do not, necessarily, faithfully depict the relativesizes or the positions of the elements therein.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of the present invention are described inreference to the drawings.

<<Embodiment 1>>

FIG. 1 shows a configuration of a magnetic field sensor according to thefirst embodiment of the present invention. In FIG. 1, a Hall element isdenoted as 1, a switch circuit is denoted as 2, a voltage amplifier isdenoted as 3, a capacitor which is a memory element is denoted as 4 anda switch is denoted as 5.

The Hall element 1 is a Hall element in a plate form with fourterminals, and the form of the Hall element 1 is geometricallyequivalent.

The first phase signal (a) that has a pulse in the first phase is givento the switch 5 and the switch circuit 2. The second phase signal (b)that has a pulse in the second phase is given to the switch circuit 2.

The timing chart in the first embodiment is shown in FIG. 7.

With respect to the magnetic field sensor constructed as the above, theoperation is described in the following.

The operation of the first phase is described.

In the first phase, the switch 5 is closed.

At this time, a power source voltage is applied across the terminalsA-A′ of the Hall element 1, and the output voltage across the terminalsB-B′ is outputted through the switch circuit 2. The output voltage ofthis Hall element 1 is inputted into the voltage amplifier 3.

The voltage amplifier 3 outputs the voltage which is proportional to theoutput voltage Vh of the Hall element 1. The output voltage V1 of thevoltage amplifier 3 in the first phase can be represented in thefollowing equation:

V 1=β(Vh+Voff 3)  (9)

Voff3 is an input offset voltage of the voltage amplifier 3 while β is avoltage amplification factor of the voltage amplifier 3. Both ends ofthe capacitor 4 are charged to the output voltage V1 of the voltageamplifier 3 via the switch 5.

Next, the operation in the second phase is described.

In the second phase, the switch 5 is open.

The power source voltage is applied across the terminals B-B′ of theHall element 1 and the output voltage across the terminals A-A′ isoutputted via the switch circuit 2. The output voltage of this Hallelement 1 is inputted to the voltage amplifier 3. The output signal ofthis Hall element which is inputted into the input terminal of thevoltage amplifier 3 becomes, substantially, of the opposite direction tothat in the first phase. Accordingly, at this time, the output voltageV2 of the voltage amplifier 3 can be represented in the followingequation:

V 2=β(−Vh+Voff 3)  (10)

In the second phase, the voltage across the terminals of the capacitor 4is maintained and is added in vector to the output voltage of thevoltage amplifier 3. The signal V, as a result of vector addition, isoutputted from the output terminals 20, 21.

Accordingly, the output voltage V of the first embodiment in FIG. 1 canbe represented in the following equation:

V=−V 1+V 2=−2βVh  (11)

It can be seen that, in the output voltage V, the input offset voltageVoff3 is canceled.

Judging from the comparison of the equations (4), (8) and (11), thoughall of the input offset voltages Voff are canceled in the same manner,the magnetic field sensor according to the present invention has a morecompact and simpler circuit configuration in comparison with the priorart of FIG. 5.

In addition, the present invention outputs an amplified signal of thedetected signal by the Hall element in two steps (first phase and secondphase), which is fewer than the number of steps (three) of the secondprior art as shown in FIGS. 6 and 8.

For example, in a device, wherein a magnetic field sensor of the presentinvention is applied, which outputs an amplified signal of the detectionsignal by the Hall element once for every constant period, powerconsumption can be reduced during a constant period in comparison withthe device which uses a magnetic field sensor in FIG. 6 by halting thepower source supply to the magnetic field sensor during the period whenthe magnetic field sensor is not in operation.

<<Embodiment 2>>

FIG. 2 shows a configuration of a magnetic field sensor according to thesecond embodiment of the present invention. In FIG. 2 a Hall element isdenoted as 1, a switch circuit is denoted as 2, a voltage amplifier isdenoted as 3, capacitors which are memory elements are denoted as 4, 6and 7, and switches are denoted as 5 and 8.

The Hall element 1 is a Hall element in a plate form with fourterminals, and the form of the Hall element 1 is geometricallyequivalent.

The voltage amplifier 3 is formed of a single input amplifier and tworesistances 22, 23 which define the amplification factor (feed backamount). This is the same as the voltage amplifier 3 of the firstembodiment with respect to the function which outputs a voltageproportional to the input voltage.

In the first phase, the first phase signal (a) which has a pulse isgiven to the switch 5 (including the switch 5 which forms a part of theswitch circuit 2) and a changing switch of a circuit which applies thepower source voltage to the Hall element 1 (included in the switchcircuit 2 and not shown). In the second phase, the second phase signal(b) which has a pulse is given to the switch 8 (forming a part of theswitch circuit 2) and a changing switch of a circuit which applies thepower source voltage to the Hall element 1 (included in the switchcircuit 2 and not shown).

The timing chart in the second embodiment is the same as the timingchart of FIG. 7.

As for the magnetic field sensor formed as above, the operation isdescribed in the following.

The operation in the first phase is described. In the first phase, theswitch 5 is closed while the switch 8 is open.

At this time, the power source voltage is applied across the terminalsA-A′ of the Hall element 1 and the output voltage Vh across theterminals B-B′ is outputted to the switch circuit 2. The output voltageVh of this Hall element 1 is applied to the capacitor 6 through theswitch 5 so as to charge the capacitor 6.

At this time, the voltage across both ends of the capacitor 7 isinputted into the input terminal of the voltage amplifier 3 through theswitch 5.

One input terminal of a single output-type voltage amplifier 31 whichforms the amplifier 3 is connected to one output terminal of themagnetic field sensor.

The single output-type voltage amplifier 31 outputs a voltageproportional to the voltage across both ends of the capacitor 7. Asdescribed below, the voltage across both ends of the capacitor 7 is Vh.The output voltage V1 of the voltage amplifier 3 in the first phase canbe represented in the following equation. This is the same as the aboveequation (9).

V 1=(Vh+Voff 3)  (12)

Here, β, Vh and Voff3 are defined in the same manner as in the firstembodiment.

Both ends of the capacitor 4 are charged to the output voltage V1 of thevoltage amplifier 3 via the switch 5.

Next, the operation in the second phase is described.

In the second phase, the switch 8 is closed while the switch 5 is open.

At this time, the power source voltage is applied across the terminalsB-B′ of the Hall element 1 and the output voltage Vh across theterminals A-A′ is outputted to the switch circuit 2. The output voltageVh of this Hall element 1 is applied to the capacitor 7 through theswitch 8 so as to charge the capacitor 7.

At this time, the voltage across both ends of the capacitor 6 isinputted to the input terminal pair (input terminal of the singleoutput-type voltage amplifier 31 and minus output terminal 21 of themagnetic field sensor) of the voltage amplifier 3 through the switch 8.

The single output-type voltage amplifier 31 outputs a voltageproportional to the voltage across both ends of the capacitor 6. Thevoltage across both ends of the capacitor 6 is Vh. The output voltage V2of the voltage amplifier 3 in the second phase can be represented in thefollowing equation. This is the same as the above equation (10).

V 2=β(−Vh+Voff 3)  (13)

In the second phase, the voltage across the terminals of the capacitor 4is maintained and is added in vector to the output voltage of thevoltage amplifier 3. The signal V as a result of the vector addition isoutputted from the output terminals 20, 21.

Accordingly, the output voltage V of the second embodiment in FIG. 2 canbe represented in the following equation.

V=−V 1+V 2=−2βVh  (14)

It can be seen that, in the output voltage V, the input offset voltageVoff3 is canceled.

The magnetic field sensor of the second embodiment repeatedly carriesout the above operation.

In this manner, according to the present invention, the output voltageVh across the output terminals B-B′ is once stored in the capacitor 6 inthe first phase. In the second phase, the connection between thecapacitor 6 and the Hall element is cut and one terminal of thecapacitor 6 is connected to the minus output terminal 21 of the magneticfield sensor while the other terminal of the capacitor 6 is connected tothe non-inverted (plus) input terminal of the single output-typeamplifier 31.

In the same manner, the output voltage across the output terminals A-A′is stored in the capacitor 7 in the second phase. In the first phase,the connection between the capacitor 7 and the Hall element is cut andone terminal of the capacitor 7 is connected to the minus outputterminal 21 of the magnetic sensor while, at the same time, the otherterminal is connected to the non-inverted input terminal of the singleoutput-type amplifier 31.

Since the capacitor 6 maintains the voltage across both terminals beforeand after the connection switching of both terminals, the output voltageVh across the terminals A-A′ and B-B′ of the Hall element 1 is convertedto the voltage Vh with the potential of the minus output terminal 21 asa reference (conversion of the offset level).

Thereby, a single output-type amplifier of a single input can beutilized as the voltage amplifier 3 in place of a double output-typeamplifier of a differential input.

The potential of said minus output terminal may be the referencepotential or may not be a reference potential. A plus output terminalmay be used in place of the minus output terminal (in this case, theoutput signal of the single output amplifier is outputted from the minusoutput terminal).

In the second embodiment, after disconnecting the capacitor 6 or 7 fromthe Hall element 1, the voltage across both ends of the capacitor 6 or 7is inputted to the single output-type amplifier 31. Thereby, thedifferential voltage between the two terminals of the Hall element canbe maintained and the disconnected Hall element 1 can operate normally.

In this manner, a single output-type amplifier can be utilized in placeof a conventional double output-type amplifier.

In addition, in a magnetic field sensor of which the potential of theminus output terminal is not a constant reference potential (includingthe ground) a single output-type amplifier can be utilized according tothe present invention.

Preferably, feed through measures are taken for the switches ofEmbodiment 1 or Embodiment 2. The switches, for which the feed throughmeasures are taken, prevent the charge stored in the parasiticcapacitance across the gate and the source, or across the gate and thedrain of the switches, from flowing out into or flowing in from thecapacitor 6 or 7 when the gate terminals of these switches are changed.

FIG. 4 is a diagram wherein feed through measures are taken for abi-directional switch 50 of the MOS structure, of which the gate isdriven by a binary voltage.

In the switches 50, 51 and 52, N channel and P channel MOS transistorsare connected in parallel, while the gate of each transistor is drivenby a binary voltage given from the outside of these switches. Here, theinput and output parts of the switches 51 and 52 are connected incommon. In addition, the switch 51 is connected to one of theinput/output part of the switch 50 while the switch 52 is connected tothe other input/output part of the switch 50. When the voltage of thegate terminal of the switch 50 changes, the charge moves which is storedin the parasitic capacitance across the source, the drain and the gateof each of the N channel and P channel MOS transistors of the switch 50.Therefore, the switches 51, 52 are driven by a binary voltage of thepolarity that is opposite to that of the binary voltage which drives theswitch 50. Thereby, the charge of the parasitic capacitance in theswitches 51, 52 is moved in the direction opposite to that of the switch50. Through this movement of the charge, the movement of the charge inthe switch 50 can be canceled.

Preferably, at least one of the resistances which define the gains ofthe voltage amplifiers of Embodiment 1 or Embodiment 2 is formed of thesame material as that of the Hall element. For example, citing thevoltage amplifier 3 of FIG. 2 as an example, the resistance 22 insertedbetween the output terminal of the single output-type amplifier 31 andthe inverted (minus) input terminal of amplifier is formed of the sameelement as the Hall element 1.

For example, N-type impurities are diffused into a P-type semiconductorsubstrate so as to form a Hall element and a resistance 22 and aresistance 23 is formed of a polysilicon resistance which has littledispersion.

In a magnetic field sensor which includes a Hall element 1 and a voltageamplifier 3 on the same semiconductor chip, when the resistance value ofthe Hall element 1 is small, the output voltage of the Hall element 1becomes large, the resistance value of this resistance 22, which is madeof the same element, also becomes small and, as a result, the gain ofthe voltage amplifier 3 becomes small. On the contrary, when theresistance value of the Hall element 1 is large, the output voltage ofthe Hall element 1 becomes small, the resistance value of thisresistance 22, which is made of the same element, also becomes largeand, as a result, the gain of the voltage amplifier 3 becomes large.

Thereby, the gain of the voltage amplifier 3 suppresses the dispersionof the output voltage of the terminals 20, 21 in accordance with thedispersion of the output voltage of the Hall element 1 due to thedispersion of the resistance value of the Hall element 1. A magneticfield sensor of which the output voltage dispersion of the terminals 20,21 is small, can be attained.

<<Embodiment 3>>

FIG. 3 illustrates a magnetic field sensor of the third embodiment whichuses the magnetic field sensor of the first embodiment according to thepresent invention. The magnetic field sensor of the third embodimentoutputs a binary digital signal of 0 or 1 in accordance with theintensity of the magnetic field.

In FIG. 3, a Hall element is denoted as 1, a switch circuit is denotedas 2, a voltage amplifier is denoted as 3, a capacitor which is a memoryelement is denoted as 4, a switch (which is closed in the first phaseand is open in the other phase) is denoted as 5, a comparator is denotedas 13, a latch circuit is denoted as 14, a clock generation circuit isdenoted as 15, the first phase clock generation circuit is denoted as 16and the second phase clock generation circuit is denoted as 17.

The Hall element 1 has a plate form with four terminals, and the form ofthe Hall element 1 is geometrically equivalent.

(a) in FIG. 7 shows a waveform (including the first phase) of the outputsignal obtained from the first phase clock generation circuit 16 while(b) in FIG. 7 shows a waveform (including the second phase) of theoutput signal obtained from the second phase clock generation circuit17.

With respect to the magnetic field sensor formed as described above, theoperation is described in the following.

In this description, the case is assumed that a constant magnetic fieldpasses through the Hall element 1 and the output voltage of the Hallelement is constant when the offset is not taken into consideration.

First, a clock which determines the first phase is generated in thefirst phase clock generation circuit 16. Next, by using this clock, avoltage is applied across the terminals which make a pair on a diagonalline of the Hall element 1, so that an output voltage of the Hallelement which is proportional to the magnetic field strength isgenerated across the other two terminals. The switch circuit 2 isoperated so that this output voltage is applied to the two inputterminals of the voltage amplifier 3. At this time, a voltage which isproportional to the output voltage of the Hall element 1 is generated inthe output of the voltage amplifier 3, which is taken into the capacitor4 via the switch 5 controlled by the first phase clock generationcircuit 16. After the end of the first phase, the switch circuit 5 isopened and the output voltage of the voltage amplifier 3 in the firstphase is maintained in the capacitor 4.

Next, a clock which determines the second phase is generated in thesecond phase clock generation circuit 17. Next, by using this clock, avoltage is applied across the terminals of the Hall element 1 whereinthe output voltage across these terminals of the Hall element ismeasured in the first phase, and the other two terminals are connectedto the voltage amplifier 3. In addition, the switch circuit 2 isoperated so that the output voltage of the Hall element, which hasopposite polarity (positive or negative) to that in the first phase, isgiven to the input of the voltage amplifier 3. At this time, the outputvoltage from the voltage amplifier 3 is the reverse voltage of that inthe first phase. In addition, since the switch 5 is open, the vector sumof the output voltage of the voltage amplifier 3 in the first phasewhich is stored in the capacitor 4 and the output voltage of the voltageamplifier 3 in the second phase is connected across the input terminalsof the comparator 13.

Then, the differential voltage applied to the input terminals of thephase comparator 13 in this second phase becomes, as described above, −2Vh with the input offset voltage Voff3 being canceled.

This value is compared with the reference value set in the comparator 13and the judgment result (A digital signal is 0 in the case that thisvalue is smaller than the reference value and a digital signal is 1 inthe case that this value is larger than the reference value.) isoutputted to the output terminal of the comparator 13.

The latch circuit 14 is connected to the second phase clock generationcircuit 17 and is set so as to latch the input voltage at the end timingof the second phase. Accordingly, a constant value (digital value of 0or 1), which is maintained until the end time of the next second phase,is outputted to the output terminal 18.

In addition, it is preferable to return the output value of this outputterminal 18 to the comparator 13 so as to set a hysteresis in thejudgment reference value for chattering prevention.

The present invention cancels the input offset voltage of the amplifierwith a simple circuit. Thereby, the advantageous effects can be obtainedattaining a compact and inexpensive magnetic field sensor which receivesno influence of that input offset voltage and has little dispersion.

In addition, according to the present invention, an advantageous effectcan be obtained attaining a magnetic field sensor of low powerconsumption.

The present invention converts the output signal of the differentialvoltage of the Hall element into a voltage relative to the referencepotential, or the like, with a simple circuit and inputs this voltage,relative to the reference potential, or the like, into a singleoutput-type amplifier.

Thereby, a magnetic field sensor is attained wherein the output signalof the differential voltage of the magnetic field sensor is amplified bya single output-type amplifier of which the circuit of the output partis simple and occupies a small chip area.

According to the present invention, an advantageous effect can beobtained attaining a compact and inexpensive magnetic field sensor.

According to the present invention, a magnetic field sensor can beattained wherein a compact memory element is used, which is suitable foran IC. Thereby, an advantageous effect can be obtained attaining acompact and inexpensive magnetic field sensor.

According to the present invention, an advantageous effect can beobtained attaining a magnetic field sensor of which the dispersion ofthe output voltage due to the dispersion of the capacitance of thecapacitor is small.

According to the present invention, an advantageous effect can beobtained attaining a magnetic field sensor wherein the dispersion of theoutput voltage is smaller than the dispersion of the resistance value ofthe Hall element.

Though the invention is described with respect to preferable modes, to acertain degree of detail, the present disclosure contents of thosepreferable modes should be changed in the details of the configurationand the modification of the combination or the order of respectiveelements can be attained without deviating from the claimed scope andthe spirit of the invention.

What is claimed is:
 1. A magnetic field sensor characterized bycomprising: a magnetic field element which outputs a signal inaccordance with an applied magnetic field strength; an amplifier whichamplifies the output signal of this magnetic field element and outputs avoltage signal across a pair of output terminals; a condenser of whichboth ends are connected to the pair of output terminals of saidamplifier; a switch which is inserted and makes a connection between oneof said output terminals in the pair and one terminal of said condenserand which is closed by a first period of a signal given from an outsideof said switch and is opened by a second period of a signal given fromthe outside of said switch; and a pair of output terminals which outputsthe voltage across the ends of said switch wherein the polarities of thevoltage signals for the pair of output terminals of said amplifier atthe first period of said signal and at the second period of said signalare mutually opposite polarities.
 2. A magnetic field sensor accordingto claim 1, characterized in that the magnetic field element is a Hallelement.
 3. A magnetic field sensor characterized by comprising: amagnetic field element which outputs a signal in accordance with anapplied magnetic field strength; an amplifier which amplifies a signalfrom this magnetic field element, which polarities in a first signalperiod and in a second signal period are mutually opposite, and outputsa voltage signal across a pair of output terminals; a condenser of whichboth ends are connected to the pair of output terminals of saidamplifier; a switch which is inserted and makes a connection between oneof said output terminals in the pair and one terminal of said condenser,and which is closed at the first signal period and is opened at thesecond signal period; and a pair of output terminals which outputs thevoltage across the ends of said switch.
 4. A magnetic field sensoraccording to claim 3, characterized in that the magnetic field elementis a Hall element.
 5. A magnetic field sensor according to claim 3,characterized by further comprising a switch circuit which switches thevoltage outputted from said magnetic field element to have oppositepolarities in a first signal period and a second signal period and whichoutputs the switched voltage.
 6. A method for detecting magnetic fieldcomprising the steps of: (a) outputting a signal according to an appliedmagnetic field strength through a magnetic field element; (b) amplifyinga signal of a first signal period of a polarity from this magnetic fieldelement for outputting a voltage signal across a pair of outputterminals of an amplifier and inputting a signal of the pair of outputterminals of the amplifier to both ends of a condenser; and (c)amplifying a signal of a second signal period of the other polarity fromthis magnetic field element for outputting a voltage signal across apair of output terminals of the amplifier and inputting a signal of oneoutput terminal in the pair to one end of the condenser, and outputtinga signal across the other end of the condenser and the other outputterminal of the amplifier to a second pair of output terminals,respectively.
 7. A method for detecting magnetic field according toclaim 6, characterized in that the magnetic field element outputs asignal in accordance with a Hall effect.
 8. A method for detectingmagnetic field according to claim 6, characterized by further comprisinga step of: (d) halting a power source supply to the magnetic fieldsensor in every constant period.